Ultrastructural changes in the ovaries of infant mice deprived of endogenous gonadotrophins and after substitution with FSH

Polymorphisms in gonadotropin and gonadotropin receptor genes as markers of ovarian reserve and response in in vitro fertilization

Since gonadotropins are the fundamental hormones that control ovarian activity, genetic polymorphisms may alter gonadal responsiveness to glycoproteins; hence they are important regulators of hormone activity at the target level. The establishment of the pool of primordial follicles takes place during fetal life and is mainly under genetic control. Consequently, single nucleotide polymorphisms (SNPs) in gonadotropins and their receptors do not seem to be associated with any significant modification in the endowment of nongrowing follicles in the ovary. Indeed, the age at menopause, a biological characteristic strongly related to ovarian reserve, as well as markers of functional ovarian reserve such as anti-Müllerian hormone and antral follicle count, are not different in women with different genetic variants. Conversely, some polymorphisms in FSH receptor (FSHR) seem to be associated with modifications in ovarian activity. In particular, studies suggest that the Ser680 genotype for FSHR is a factor of relative resistance to FSH stimulation resulting in slightly higher FSH serum levels, thus leading to a prolonged duration of the menstrual cycle. Moreover, some FSHR gene polymorphisms show a positive association with ovarian response to exogenous gonadotropin administration, hence exhibiting some potential for a pharmacogenetic estimation of the FSH dosage in controlled ovarian stimulation. The study of SNPs of the FSHR gene is an interesting field of research that could provide us with new information about the way each woman responds to exogenous gonadotropin administration during ovulation induction.

Gene expression profiling during early folliculogenesis in the mouse ovary

OBJECTIVE

To evaluate genes involved in ovarian primordial-to-primary follicle transition.

DESIGN

Experimental animal study.

SETTING

Research institute.

ANIMAL(S)

Day-2 and day-4 female Swiss mice.

INTERVENTION(S)

We conducted a complementary DNA array study using ovarian messenger RNAs from day-2 and day-4 mice.

MAIN OUTCOME MEASURE(S)

The expression profiles of 1,176 genes in neonatal mouse ovaries on day 2 and day 4, which contain primordial and primary follicles, respectively, were compared.

RESULT(S)

Twenty-six percent of genes were differentially expressed between day-2 and day-4 ovaries, with 19% being up-regulated and 7% down-regulated in day 4. Analysis of differentially expressed genes revealed that the primordial-to-primary follicle stage transition is associated with induction in the expression of mainly growth factors, immune-related factors, hormone and hormone receptors, and signal transducers. The transition is also associated with proliferation of granulosa cells and absence of apoptosis. In addition, our studies demonstrated that the primary follicles express estrogen receptor beta and are responsive to estrogen actions in vitro in terms of increase in the number of primary follicles and granulosa cell proliferation.

CONCLUSION(S)

The transition of primordial to primary follicles is associated with the participation of multiple pathways in regulating gene expression.

Stepwise requirement of c-kit tyrosine kinase in mouse ovarian follicle development

Ovarian follicle development is controlled by the cycling variation of gonadotrophins derived from the central nervous system. Intragonadal signals are also required, especially in the autonomous development of small follicles. Receptor tyrosine kinase c-kit and its ligand SLF (Steel factor) are expressed on the surface of specific populations of follicle-forming cells in a contiguous manner and are thought to have important roles in follicular development. We blocked the interaction of c-kit and its ligand by administering the function-blocking antibody ACK2 to developing mice at various times after birth and monitored ovarian follicle development. A blockade of c-kit function disturbed the onset of primordial follicle development, primary follicle growth, follicular fluid formation of preantral follicles, and penultimate-stage ovarian follicle maturation before ovulation. Ovarian follicle growth was dependent on c-kit during the first 5 days after birth when the functional FSH receptor is not yet expressed in mouse ovary. In contrast, primordial follicle formation and survival, small preantral or antral follicle development, ovulation, and luteinization of the ovulated follicle were not affected by this antibody. These findings indicate the stepwise requirement of c-kit and its ligand interaction system in the developing ovarian follicle and that c-kit with its ligand supports the autonomous development of ovarian follicle independent of gonadotrophins.

Protective effects of D-Trp6-luteinising hormone-releasing hormone microcapsules against cyclophosphamide-induced gonadotoxicity in female rats

The possible protective effect of an agonist of luteinising hormone-releasing hormone (LH-RH) against the ovarian damage caused by cyclophosphamide was investigated in rats. D-Trp6-LH-RH microcapsules were injected once a month for 3 months, in a dose calculated to release 25 micrograms day-1. Control animals received the injection vehicle. Sixty days after the first injection of microcapsules, cyclophosphamide was given at a loading dose of 50 mg kg-1 followed by 5 mg kg-1 day-1 for 30 days, while the treatment with D-Trp6-LH-RH was continued. When the ovaries were examined 3 months and 5 months after discontinuation of treatment, a significant reduction in the total number of follicles (P less than 0.01) was found in non-pretreated animals given cyclophosphamide. This reduction affected mainly follicles larger than 100 microns. An irreversible disintegration and destruction of granulosa cells was also observed in this group. In animals pretreated with D-Trp6-LH-RH, administration of cyclophosphamide caused no reduction in the number and diameter of follicles. Thus, the treatment with D-Trp6-LH-RH microcapsules before and during chemotherapy prevented the ovarian injury inflicted by cyclophosphamide. The suppression of gonadal function by LH-RH analogues could be possibly utilised for the protection of the ovaries against damage caused by cytotoxic drugs.

Development of naked growing mouse oocytes in vitro

Half grown oocytes were released from follicles of 7-day-old mouse ovaries during overnight culture. Naked oocytes free of attached follicular cells were cultured in MEM plus 10% fetal calf serum over the developing monolayer of ovarian cells. Oocytes increased in diameter for a period of at least a week at 1.6 micron per day, or 70% of the in vivo growth rate. The ultrastructure of cytoplasmic organelles in cultured growing oocytes was normal. During the second week, about 35% underwent spontaneous fragmentation, and at least 10-20% resumed meiotic maturation. We conclude that a significant fraction of naked oocytes reached a functional state comparable to that of normal full grown oocytes at a rate approaching the in vivo rate. Free oocytes with attached cells grew to a larger average diameter than naked oocytes, and incorporated 3H-leucine 75% more rapidly. Naked oocytes cultured in the absence of ovarian cells did not grow, and died when pyruvate was omitted from the medium. Naked oocytes did not grow when cultured over primary mouse fibroblasts, L-cells, CHO cells, or hepatoma cells. Naked oocytes separated from the monolayer of ovarian cells by a 0.7 mm layer of agar grew at 60% of the rate of control oocytes.

The role of the endocrine thymus in female reproduction

Neonatal thymectomy in mice induces ovarian disturbances, indicating some relationship between the thymus and the ovaries. The mechanism of the relationship, however, is not fully understood. One approach to elucidating the complex relationship has been to measure circulating hormone levels in thymectomized animals and those with small thymus glands, and compare these levels with those found in control animals. The data indicate that a thymus-pituitary-ovarian axis exists and that thymus disturbances may hasten the aging processes of the ovaries.

Effect of neonatal thymectomy on follicle numbers in the post-natal mouse ovary

1. Surgical removal of the thymus gland within 48 hours of birth has no effect upon the numbers of small, medium and large ovarian follicles in Bagg albino strain mice during the first 12 weeks of life. 2. 20% of thymectomised mice more than 12 weeks of age developed ovarian atrophy which included the disappearance of corpora lutea and an overall reduction in all fractions of the follicle population. 3. These results do not support the proposal of Nishizuka and Sakakura that the thymus gland specifically maintains the non-growing, small (primordial) follicle pool in the mouse ovary during post-natal and reproductive life.

Ovarian development in athymic nude mice. IV. The effect of PMSG and oestradiol on the growth of the oocyte and follicle

Retarded follicular and oocyte nucleolar growth rates in ovaries of 1 month old congenitally athymic nude mice are restored by pregnant mare serum gonadotrophin (PMSG). By contrast oestradiol-17beta depresses follicular growth rate in phenotypically normal (control) mice to levels found in nude littermates. Paradoxically, oestradiol-17beta stimulates nucleolar growth rate in control mice, but not nudes, to levels found in PMSG treated groups. These results are discussed in relation to the position of the thymus gland in the pituitary/ovarian axis and the mode of action gonadotrophin upon oocyte and follicular growth in the pre-puberal mouse ovary.

Ovarian development in athymic nude mice. III. The effect of PMSG and oestradiol upon the size and composition of the ovarian follicle population

The response of 1 month old congenitally athymic nude mice and their phenotypically normal littermates to exogenous pregnant mare serum gonadotrophin (PMSG) and oestradiol-17beta has been tested. An equal increase in the number of growing follicles was detected in both nudes and controls in response to PMSG. A specific increase occurred in the number of unilaminar follicles in the initial growth stages in addition to the increase in the number of multilaminar and vesicular follicles. Oestradiol depressed follicular growth equally in both nudes and controls. The contracted appearance of growing follicles in nudes disappeared under the influence of PMSG and was induced in ovaries of control mice treated with oestradiol. We conclude that the ability of the mouse ovary to respond to exogenous PMSG and the oestradiol is not impaired by congenital athymia as expressed in the nude genotype. The data suggest that the retardation of follicular growth already reported in 1 month old nudes arises from a deficiency of gonadotrophin.